Whitewater recovery process

ABSTRACT

Whitewater recovery processes, and associated systems and components, are generally described. Certain embodiments relate to whitewater recovery processes in which ion exchange is used to remove dissolved ions from the whitewater, which can reduce the degree to which chemical additives are used in the process. In certain embodiments, flocculation and/or filter components can be employed to aid in the removal of suspended solids from the whitewater.

RELATED APPLICATIONS

This application is a continuation of U.S. patent application Ser. No.13/801,306, filed Mar. 13, 2013, and entitled “Whitewater RecoveryProcess,” which is incorporated herein by reference in its entirety forall purposes.

FIELD OF INVENTION

Whitewater recovery processes, and associated systems and components,are generally described.

BACKGROUND

In traditional papermaking processes, water is introduced to the papermaking system as a carrier fluid. The carrier fluid is used to suspendwood fibers, suspension aids, filler materials, and the like as aslurry, which is spread evenly over a wire web. The carrier fluid isdrained, squeezed (e.g., using nips), and vacuumed away from the web,while most of the fillers, fibers, and retention aids remain on the weband eventually form the paper sheet. The water that is drained away fromthe paper sheet is called whitewater, due to the high residual fiber,filler, and brightener content, which imparts a white color to the waterin some cases.

Papermaking processes generally utilize large amounts of water, withtypical usages ranging from 200 gallons per ton of paper for highlyrecycled paper board to 30,000 gallons per ton of paper for specialtyfine paper. In the early days of paper making, fresh water was routinelyconsumed from rivers and lakes to produce the paper. However, such largeamounts of fresh water consumption were harmful to the environment. Tolimit environmental damage, there has been a movement to reduce freshwater use and reduce wastewater discharges from pulp and papermanufacturing facilities.

Current pulp and paper mills implement numerous whitewater reusestrategies. Most of these strategies clean the recycled wastewater usingsimple suspended solids clarification, filtration, and screeningtechniques. The reduction in fresh water make-up to the paper machinehas resulted in a substantial increase in concentration of thecontaminants in the whitewater system. The recovered water is generallyused many times before it is finally discharged. Simple suspended solidsclarification, filtration, and screening techniques do not address theincrease in dissolved and colloidal solids in the whitewater loops. Inmany current systems, chemical additives are fed to the whitewaterstream in an attempt to control organic material, colloidal solid, anddissolved ion accumulation. However, many typical reuse strategies areunable to effectively remove fine colloidal substances, total dissolvedsolids (including scale causing ions), and foulants such as ironaluminum and bacteria. As a result, a significant amount of dissolvedand colloidal substances introduced by the paper process are allowed tocycle up in concentration as the whitewater is continuously reused andas fresh water make-up is reduced. This can cause numerous problems inthe paper machine, paper product, and in other areas of the mill. Forexample, as sparingly soluble salts cycle up in concentration, they mayeventually precipitate and scale. As colloidal anionic particles(commonly referred to as anionic trash) cycle up in concentration, theymay inhibit the flocculation and removal of suspended solids, leading tothe fabrication of an inferior paper product. In addition, the buildupof total dissolved solids (TDS) and especially anionic colloidal trashadversely affects the performance of retention aids, which are chemicaladditives that promote the retention of fibers on the paper web anddewatering of the paper product when the wet slurry is undergoing thedewatering process. If the fibers on the web do not dewater properly,drainage aids are sometimes applied. The increased contaminant load inthe whitewater reduces the effectiveness of the drainage aids. As aresult, the paper sheet in production has a higher moisture content,which can increase the amount of heat energy that is required to be usedto dry the paper in the dryer section of the paper machine. The energyincrease can be substantial and costly.

Two basic techniques are primarily utilized to control the buildup ofsparingly soluble salts and anionic colloidal substances. One suchtechnique involves chemical addition. For example, sequestrationchemicals can be added to complex or chelate multivalent cations so theycan no longer easily bind with counter ions such as sulfate andcarbonate to form scale. Another technique involves chemical softening.This technique is based on the principal that raising the pH of asolution in the presence of alkaline ions brings the sparingly solublesalts to their saturation point. This causes the salts that are presentto precipitate as a solid for subsequent removal by sludge dewateringsystems.

The addition of chemical additives to process whitewater can causeseveral problems. For example, continuous addition of chemical additivesis necessary to control scaling and fouling. Continual addition ofchemical additives is also needed to compensate for increasingconcentrations of contaminants in the whitewater loops. The chemicalsare in part charge neutralized by the increased contaminant load in thewhitewater. The excess chemical consumption is costly to the mill andcauses a buildup of total dissolved solids (TDS), which make thewhitewater difficult to treat when it is finally discharged. The buildupof chemical additives and background salts has a significant negativeeffect on mill production, sheet quality, and consumption of heatenergy, as described above. Chemical additives that are used intraditional whitewater recycling processes are also consumed in part bythe anionic trash within the whitewater, as the anionically chargedcolloids attach to the cationic chemical additives. Because the anionictrash consumes the chemical additives, the chemical additives must beadded in excess, which can increase the degree to which additivesaccumulate in the process. Systems and methods for whitewaterclarification that do not involve the addition of large amounts ofchemical additives would be desirable.

SUMMARY OF THE INVENTION

Whitewater recovery processes and associated systems and components aregenerally described. Certain embodiments relate to whitewater recoveryprocesses in which selective ion exchange is used to remove dissolvedions from the whitewater, which can reduce the degree to which chemicaladditives are used in the process. In certain embodiments, flocculationand/or filter components can be employed to aid in the removal ofsuspended solids from the whitewater. Certain of the inventive systemsand methods described herein achieve a balance between contaminantremoval techniques and reduced addition of chemical additives, whichultimately enhances the profitability and effectiveness of the paperproduction process. The subject matter of the present inventioninvolves, in some cases, interrelated products, alternative solutions toa particular problem, and/or a plurality of different uses of one ormore systems and/or articles.

In one aspect, a system for the recovery of whitewater containingcations and suspended solids is provided. The system comprises, in someembodiments, a flocculation vessel containing a flocculent able toagglomerate the suspended solids to form agglomerations of theflocculent and the suspended solids upon exposure of the flocculent to aliquid input stream comprising whitewater or derived from whitewater,the flocculation vessel configured to produce a supernatant streamcontaining a lower quantity of suspended solids than the liquid inputstream; a filter configured to receive at least a portion of thesupernatant stream, the filter configured to produce a retentate streamand a filtrate stream, the filtrate stream containing a lower quantityof suspended solids than the retentate stream; and an ion exchangevessel configured to receive at least a portion of the filtrate stream,the ion exchange vessel containing an ion exchange medium configured toremove at least a portion of the cations from the filtrate stream. Incertain embodiments, a method of treating whitewater is provided. Themethod comprises, in certain embodiments, exposing a liquid input streamcomprising whitewater or derived from whitewater and containing cationsand suspended solids to a flocculent such that agglomerations offlocculent and suspended solids are formed; removing at least a portionof the agglomerations from the liquid input stream to produce asupernatant stream containing a lower quantity of suspended solids thanthe liquid input stream; filtering the supernatant stream to produce aretentate stream and a filtrate stream containing a lower quantity ofsuspended solids than the retentate stream; and removing at least aportion of the cations from the filtrate stream using an ion exchangemedium.

In some embodiments, the method comprises flowing a liquid input streamcomprising whitewater or derived from whitewater and containing cationsthrough an ion exchange vessel containing an ion exchange medium; andremoving at least a portion of the cations from the liquid input streamusing the ion exchange medium to produce an ion exchanged effluentstream.

The method comprises, in certain embodiments, contacting a liquid streamcomprising whitewater or derived from whitewater and containing calciumcarbonate with an ion exchange medium; and adjusting or maintaining a pHof the liquid input stream at or below about 7.5 such that at least aportion of the calcium carbonate is dissolved within the liquid inputstream prior to or while being contacted with the ion exchange medium.

In certain embodiments, the method comprises exposing a liquid inputstream comprising whitewater or derived from whitewater and containingcations and suspended solids to a flocculent and a magneticallyresponsive material such that agglomerations of flocculent, magneticallyresponsive material, and suspended solids are formed; removing at leasta portion of the agglomerations from the liquid input stream using amagnet to produce a supernatant stream containing less suspended solidsthan the liquid input stream; and removing at least a portion of thecations from the supernatant stream using an ion exchange medium.

Other advantages and novel features of the present invention will becomeapparent from the following detailed description of various non-limitingembodiments of the invention when considered in conjunction with theaccompanying figures. In cases where the present specification and adocument incorporated by reference include conflicting and/orinconsistent disclosure, the present specification shall control.

BRIEF DESCRIPTION OF THE DRAWINGS

Non-limiting embodiments of the present invention will be described byway of example with reference to the accompanying figures, which areschematic and are not intended to be drawn to scale. In the figures,each identical or nearly identical component illustrated is typicallyrepresented by a single numeral. For purposes of clarity, not everycomponent is labeled in every figure, nor is every component of eachembodiment of the invention shown where illustration is not necessary toallow those of ordinary skill in the art to understand the invention. Inthe figures:

FIG. 1A is an exemplary schematic illustration of an ion exchangeprocess step of a whitewater recovery system, according to certainembodiments;

FIG. 1B is, according to certain embodiments, a schematic illustrationof an ion exchange vessel;

FIG. 2A is a schematic illustration of a whitewater recovery systemincluding a flocculation step and an ion exchange step, according tosome embodiments;

FIG. 2B is a schematic illustration of a flocculation vessel, accordingto certain embodiments;

FIG. 3 is, in accordance with certain embodiments, a schematicillustration of a whitewater recovery system;

FIGS. 4A-4C are schematic illustrations of a whitewater recovery systemand process, according to certain embodiments; and

FIGS. 5A-5C are, according to one set of embodiments, plots of theconcentration of calcium, magnesium, and manganese as a function of theduration of an ion exchange process step.

DETAILED DESCRIPTION

Whitewater recovery processes and associated systems and components aregenerally described. Certain embodiments relate to whitewater recoveryprocesses in which dissolved ions are removed from the whitewater viaion exchange, the use of which can reduce the degree to which chemicaladditives are used in the process. In certain embodiments, flocculationand/or filter components can be employed to aid in the removal ofsuspended solids from the whitewater. The flocculation and/or filtercomponents may also be operated, in certain embodiments, with little orno net addition of chemical reagents. The ability to remove suspendedsolids and dissolved ions from whitewater with limited or no netaddition of chemical reagents can provide a variety of advantages,including reducing precipitation and scaling in the paper-making system,enhancing the degree to which dewatering is achieved prior to heatdrying the paper product, and enhancing the quality of the paper that isproduced, among other benefits.

In certain embodiments, ion exchange is used to remove at least aportion of the cations within the recovered whitewater. Certainembodiments are directed to the inventive recognition that many solids(including precipitates such as calcium carbonate and other sparinglysoluble salts) can be removed by dissolving such solids within thewhitewater (for example, by adjusting the pH or other conditions withinthe whitewater) and subsequently removing the dissolved ions from thewhitewater. This is in contrast to many prior art methods, in which suchsolid material is removed using traditional solids removal methods, suchas filters and the like.

In particular, the whitewater recovery systems described herein can beused to remove cations of sparingly soluble salts (including multivalentcations ions such as Mg²⁺, Ca²⁺, Sr²⁺, Ba²⁺, Fe²⁺, Mn²⁺ and Al³⁺). Thecations of sparingly soluble salts can precipitate out within thepapermaking process and cause scaling when they are combined withcounter anions (e.g., carbonate, sulfate, hydroxide, and the like). Inaddition, the presence of multivalent ions (and especially Ca²⁺) canlower the solubility of pitch originating from the wood pulp and fibers,which can precipitate out of solution. The precipitated pitch is sticky,and can cause fouling problems within paper machines and/or on paperproducts. Removal of multivalent cations can reduce the degree to whichprecipitation and scaling occur in the papermaking process, which canreduce the frequency with which the papermaking machines must be cleanedand improve the quality of the paper. In some embodiments, the pH of thewater that is being processed is adjusted to increase the solubility ofsparingly soluble salts (such as multivalent cations), after whichadjustment, the ion exchange medium can be employed to remove thedissolved ions.

The ion exchange methods described herein can, in certain embodiments,remove cations of sparingly soluble salts without the addition ofchemical sequestration agents or with use of reduced quantities of suchmaterials compared with typical conventional whitewater recoveryapproaches. In many prior systems, ionic charge from background saltscreates a buffering effect in the whitewater that overwhelms wetstrength agents, starch modifiers, sizing chemistries, and numerousother chemical additives typically employed in the papermaking process.This makes it necessary to add these additives in excess in order toovercome the charge neutralization/buffering effect. Moreover,additional new and specialty chemicals may be required to address thebuffering effect, often at a cost premium. The continual addition ofexcess chemicals and additional specialized chemistry creates acompounding effect and results in a buildup of chemicals in thewhitewater. This makes the final effluent more difficult to treat andultimately increases contaminant loads to and salinity in theenvironment, the papermaking machine, and the paper product made by thepapermaking machine. The present ion exchange process involves a muchdifferent approach. Rather than sequestering contaminants via theaddition of chemical reagents, the ion exchange process effectivelyremoves the contaminants from the whitewater. The use of ion exchangecan thus prevent the cycling up of the concentration of the contaminantsin the whitewater as fresh water makeup flow rates are reduced.

In certain embodiments of the inventive ion exchange processes, an ionexchange medium (e.g., an ion exchange resin such as a cationic ionexchange resin) is used to remove dissolved cations of one type from thewhitewater, replacing them with cations of another type. For example,particular embodiments of the inventive ion exchange processes describedherein can be used to remove multivalent cations (e.g., Me²⁺, Ca²⁺,Sr²⁺, Ba²⁺, Fe²⁺, Mn²⁺ and/or Al³⁺) and substitute them with monovalentcations (e.g., Na⁺, K⁺, NH₄ ⁺), which are generally much more solublethan multivalent cations in many environments (e.g., in environmentswith high concentrations of carbonate and sulfate). Because themonovalent ions are much more soluble, they do not tend to precipitateor scale under typical conditions in which the whitewater is used in thepapermaking process. As one particular example, at approximately 32° C.,sodium sulfate has a solubility that is over 700 times greater than thatof calcium sulfate.

FIG. 1A is a schematic diagram illustrating whitewater recovery system100, which can be used to recover a liquid input stream 105 comprisingwhitewater or derived from whitewater. The whitewater within liquidinput stream 105 can comprise water originating from any source within apaper making process. The liquid within stream 105 can be whitewaterdirectly from a whitewater source, or whitewater that has beenpre-processed or otherwise modified. Liquid input stream 105 can containanions and/or cations, in certain embodiments. For example, liquid inputstream 105 can contain multivalent cations, such as Mg²⁺, Ca²⁺, Sr²⁺,Ba²⁺, Fe²⁺, Mn²⁺, and/or Al³⁺. Liquid input stream 105 might alsocontain suspended solids such as paper fragments (e.g., wood fiber,pulp, etc.), colloidal material (such as anionic colloidal trash), orother solid components, although in other embodiments, such contaminantsmight not be present (e.g., they may be pre-removed using, for example,flocculation and/or filtration processes, including those describedelsewhere herein). In certain embodiments, liquid input stream 105originates from an upstream process within a whitewater recoveryprocess, such as a flocculation or filtration process, as described inmore detail below. In other embodiments, liquid input stream 105originates directly from a whitewater effluent stream of a papermakingprocess.

In FIG. 1A, liquid input stream 105 is flowed through an ion exchangevessel 110 containing ion exchange medium. When liquid input stream 105is contacted with the ion exchange medium, at least a portion of thecations within liquid input stream 105 can be removed (and cationswithin the ion exchange medium can be released) to produce an ionexchanged effluent stream 115. In certain embodiments, the amount ofmultivalent cations within ion exchanged effluent stream 115 is lowerthan the amount of multivalent cations within liquid input stream 105.For example, in some embodiments, the amount of multivalent cations(e.g., any one or more of Mg²⁺, Ca²⁺, Sr²⁺, Ba²⁺, Fe²⁺, Mn²⁺, and/orAl³⁺) within the ion exchanged effluent stream 115 is at least about 70%lower, at least about 80% lower, at least about 90% lower, at leastabout 95% lower, or at least about 99% lower than the amount ofmultivalent cations within liquid input stream 105.

A variety of types of ion exchange media can be used, and there areseveral factors that are typically considered when choosing an ionexchange medium. Generally, the ion exchange medium should be configuredsuch that, upon exposure of the ion exchange medium to the whitewater,relatively undesirable ions (including certain multivalent ions) fromthe whitewater are selectively bound to the ion exchange medium. In somesuch cases, other ions within the ion exchange medium (e.g., sodium,potassium, and the like) are simultaneously released into the whitewaterin exchange for the multivalent ionic species. In many embodiments,complete removal of all ions within the ion exchange step is notnecessary or practical. For example, in many cases, the concentration ofall ionized salts within the whitewater stream would easily overwhelmthe ion exchange apparatus and require an excess of regenerationchemicals and regeneration water. The normal high salt content of thewhitewater would quickly exhaust the ion exchange medium, and the volumeof water needed to feed the regeneration reagent (required to regeneratethe ion exchange medium) would approach or surpass the volume of initialwhitewater that is being recovered, therefore making the processimpractical.

Accordingly, in certain embodiments, the ion exchange resin is chosenthat selectively removes target ions from the whitewater stream. Forexample, the ion exchange medium can be chosen such that it removes onlycomponents of sparingly soluble salts (such as multivalent ions likeMg²⁺, Ca²⁺, Sr²⁺, Ba²⁺, Fe²⁺, Mn²⁺, and/or Al³⁺). In some suchembodiments, the ion exchange medium replaces the removed ions withhighly soluble ions such as Na⁺, K⁺, and NH₄ ⁺.

Another factor that can be considered during the selection of the ionexchange medium is the flow rate of the whitewater recovery process. Incertain embodiments, the whitewater recovery process is configured toprocess relatively high flow rates of whitewater (e.g., flow rates of atleast 500 gallons per minute, up to 5,000 gallons per minute, orhigher). Accordingly, in such embodiments, it can be important to selectan ion exchange medium that is capable of allowing such flow rates toeconomically pass through the ion exchange resin while maintainingintimate contact between the resin and the whitewater. The whitewaterrecovery systems described herein are not required to treat an entirewhitewater flow. For example, in some embodiments, the recoverywhitewater system is configured such that it treats only an amount offlow that is sufficiently high to inhibit or prevent the accumulation ofcontaminants within the papermaking process. In certain embodiments, thewhitewater recovery system is configured such that the contaminantremoval rate equals or exceeds the contaminant introduction rate fromthe paper making process. Configuring the whitewater recovery process inthis way can bring the contaminants in the whitewater loops to a pointof equilibrium, thereby preventing the contaminates from cycling up inconcentration and causing scaling and fouling. In addition, configuringthe whitewater recovery process in this way can diminish the need forthe addition of excess chemical additives. The ability of a particularion exchange medium to maintain a high operating flow rate can depend onthe geometry of the ion exchange medium itself and the quantity of theion exchange sites in the resin. For example, if the ion exchange mediumcomprises beads or particles with relatively large pores (e.g.,macroreticular resins), the water (and any unwanted contaminants, suchas organic material) can more freely flow (e.g., diffuse) through thepores of the medium matrix. A high concentration of ion exchange sitesper unit volume of ion exchange medium will also allow the medium toexhibit rapid kinetics and sustain effective contaminant removal at highoperating flux. On the other hand, if the pores within the ion exchangemedium are small (as might be the case with many conventional gel ionexchange resins), the resin can trap organic materials and make itdifficult to remove the organics during normal regeneration of the ionexchange medium. Gross suspended solids contamination can cause water toflow around the medium (rather than through it), and limit theinteraction between the ions within the whitewater and the active siteswithin the ion exchange medium. This principle also illustrates why itis important to establish proper pretreatment to protect the ionexchange column and the ion exchange medium from fouling, for example,using the methods described elsewhere herein.

It is important, in certain embodiments, to select an ion exchangemedium that has a high operating capacity (i.e., they contain manyactive sites per unit volume). The use of an ion exchange medium with ahigh operating capacity can reduce the size of the ion exchange system,making it easier to integrate into a whitewater recovery process.

In some embodiments, the ion exchange medium comprises an ion exchangeresin. Ion exchange resins are generally water insoluble matrixmaterials fabricated from organic polymers. Ion exchange resins can beprovided in the form of gels, porous beads, or in any other suitableform that allows for the transport of water through the ion exchangeresin.

In certain embodiments, the ion exchange medium comprises a weak acidcation resin (i.e., an ion exchange resin that is weakly acidic). Incertain embodiments, the weak acid cation resin contains carboxylatefunctional groups. In some embodiments, the weak acid cation resincontains other weakly acidic functional groups, such asaminomthylphosphonic functional groups or iminodiacetic acid functionalgroups. Examples of suitable weak acid cation resins include, but arenot limited to, Lewatit® TP 260, Lewatit® TP 207, and Lewatit® CNP80-WSfrom Lanxess (Leverkusen, Germany); IMAC® HP336 and Dowex™ MAC-3 fromRohm and Haas Company (Philadelphia, Pa.); and SST80DL from ThePurolite® Company (Bala Cynwyd, Pa.).

The use of weak acid cation resins as the ion exchange medium can beparticularly advantageous in certain embodiments. Generally, weak acidcation resins have relatively large operating capacities. In addition,weak acid cation resins are relatively easy to regenerate compared tomany other ion exchange media. For example, unlike many conventionalstrong acid cation (SAC) resins (which are frequently used inconventional water softening), weak acid cation resins can be selectedthat are easily regenerated by adding mineral acid in an amount ofbetween about 100% and 120% percent the stoichiometric equivalent. Withmany conventional SAC resins, regeneration is generally achieved byfeeding NaCl (e.g., in a brine solution) at a level of between about200% and about 300% of the stoichiometric equivalent. The use of suchlarge amounts of NaCl can, in certain cases, result in high saltdischarges to the environment. The brine cycle can also, in certaininstances, create the potential for significant introduction of chloridein the softener effluent. This could cause considerable corrosion issuesin the downstream components, especially those that make use ofstainless steel piping and other components.

In some embodiments, the ion exchange medium comprises a strong acidcation resin (i.e., an ion exchange resin that is strongly acidic). Incertain embodiments, the strong acid cation resin contains sulfonic acidfunctional groups. Examples of suitable strong acid cation resinsinclude, but are not limited to, Lewatit® S 1667 and Lewatit® S 1668from Lanxess; Amberlite™ FPC23 H, Dowex™ Monosphere C-350, Dowex™ G-26,Dowex™ Monosphere C-10, and Dowex™ Monosphere Marathon C from Rohm andHaas Company; and SST60H and SST80DL from The Purolite® Company.

In some embodiments, the ion exchange medium comprises a chelatingresin. The chelating resin can comprise, for example, iminodiaceticacid. Suitable chelating resins include, but are not limited to, S930from The Purolite® Company and TP207 from Lanxess.

While the use of resins as ion exchange media has been primarilydescribed, it should be understood that the invention is not so limited,and in other embodiments, ion exchange media comprising a zeolite, aclay (e.g., montmorillonite clay), soil humus, or any other suitable ionexchange medium could be employed. In certain embodiments, however, theuse of resins as the ion exchange medium is preferred. For example, insome instances, zeolites can be difficult to regenerate, can exhibitmuch higher contaminant leakage, can cause particle shedding/release,and can require frequent replacement.

Ion exchange vessel 110 can assume a variety of configurations. Incertain embodiments, the ion exchange medium can be immobilized withinion exchange vessel 110 that comprises a packed column. FIG. 1B is aperspective view schematic illustration of an exemplary ion exchangevessel 110. In FIG. 1B, ion exchange medium is immobilized within vesselcompartment 120. Ion exchange vessel further comprises an inlet 125 andan outlet 130. A liquid input stream comprising whitewater or derivedfrom whitewater can be transported through ion exchange compartment 120via inlet 125, and subsequently out of ion exchange compartment 120 viaoutlet 130. The ion exchange medium can be immobilized within the ionexchange compartment, for example, by placing meshes or other screens inor near inlet 125 and/or in or near outlet 130, such that the whitewateris transported through the ion exchange medium without entraining orotherwise transporting the ion exchange medium out of ion exchangevessel 110. Suitable columns include those designed and/or manufacturedby Graver Water Systems, New Providence, N.J.; General Electric; SiemensWater Technologies (Broussard, La.); and Bayer AG (Via Lanxess). While asingle ion exchange vessel is illustrated in FIG. 1B, the invention isnot limited to the use of single ion exchange vessels, and in certainembodiments, a plurality of ion exchange vessels are employed.

By immobilizing the ion exchange medium within compartment 120, harmfulions can, in certain embodiments, be removed or partially removed fromthe whitewater stream without adding ion exchange medium or any othermaterial to the whitewater stream, thereby producing an ion exchangestream that is generally free of added chemical components (aside fromthe exchanged ions originating from the ion exchange medium).

While systems in which the ion exchange medium is contained within anion exchange vessel have been described, and while the use of vessels inwhich the ion exchange medium is contained can impart certainadvantages, it should be understood that the invention is not solimited, and that in other embodiments, the ion exchange medium can beused to process the whitewater without being contained within a vessel.For example, the ion exchange medium can be added to the whitewaterstream and subsequently filtered out of the whitewater stream withoutthe ion exchange medium being confined to a particular vessel.

In certain embodiments, removing at least a portion of the cations fromthe whitewater stream using the ion exchange medium is performed at a pHof between about 5.5 and about 8.5 or between about 5.5 and about 7.5.Operating within such a pH range can allow one to use weak acid cationion exchange media, which are stable in moderately acidic environments(and which provide several advantages including higher operatingcapacity, as discussed elsewhere herein). In addition, operating withinthis pH range increases the solubility of Ca²⁺ and other sparinglysoluble ions, relative to their solubilities at pHs outside this range.

After the whitewater has been transported through the ion exchangemedium for a period of time, the ion exchange medium can be processed toremove the collected multivalent ions and regenerated such that themedium is again capable of exchanging monovalent ions for multivalentions. For example, in certain embodiments, an acidic solution (e.g., adilute acid solution such as 0.5-4% H₂SO₄ or 5-10% HCl) can be flowedthrough the ion exchange medium, which results in the multivalent ionsbeing stripped from the ion exchange medium. This step can be used toconcentrate the multivalent ions and other contaminants into a small,manageable liquid waste stream (e.g., stream 112 in FIG. 1A), which can,in certain embodiments, be neutralized and discharged to, for example, acentral wastewater treatment plant. After removing the whitewatercontaminants, the ion exchange medium can be regenerated, for example,using the process steps described above in certain embodiments in whichweak acid cation- and strong acid cation-based ion exchange media areemployed. The ability to establish ion exchange resin selectivity forthe removal of contaminating species (such as multivalent ions), theability to strip the contaminants from the ion exchange medium forsubsequent disposal, and the ability to reuse the ion exchange mediumrepresent several significant benefits of the inventive ion exchangesystems described herein.

In certain embodiments, an alkaline solution can be used to neutralizethe ion exchange medium to maintain a neutral or near-neutral pH withinthe ion exchange apparatus and/or within the processed whitewaterflowing from the ion exchange medium. For example, in certainembodiments in which weak acid cation resins are employed, the resin isneutralized with caustic in order to maintain a near-neutral pH in theion exchange effluent and to guard against downstream chloride release.

The degree to which the effluent and operating pH of the ion exchangeapparatus is adjusted (e.g., using alkaline solution) during ionexchange medium regeneration is generally based on the needs of theparticular papermaking system in which the whitewater recovery processis being used. For example, many paper mills introduce fillers to thepulp slurry. The fillers (such as precipitated calcium carbonate (PCC)and ground calcium carbonate (GCC), talc, clay, silica, and otherfillers) are often added because they are less costly than wood fiber.PCC, GCC, and other fillers also increase the brightness of the papersheet and are often used with fine white paper products like copy paper.A slight downward shift in the pH of the whitewater easily solubilizes asignificant portion of the PCC and/or the GCC. In such cases, the CO₃portion of the PCC and GCC dissolves and is converted to CO₂, which issubsequently released from the ion exchange column. As the pH of thesolution drops from 8 to 7, the amount of dissolved calcium increases byapproximately 2 orders of magnitude. The pH of the solution as it passesthrough the weak acid cation (WAC) resin can be reduced by the acidicenvironment of the weak acid cation resin. The greater the downwardshift in pH, the greater the increase in dissolved calcium.

The dissolution of PCC and GCC can be especially important, for example,for fine white paper production and for the box industry. Once the PCCor GCC is introduced to the paper machine, it predominantly leaves thepaper machine as product, and its task is complete. Residual PCC and GCCcan, in certain instances, pass through the web of the paper productionprocess and may be present in the whitewater. The whitewater is thenoften reused. When it is returned to the paper machine it can come incontact with size chemistry. A common size agent, alkyl succinicanhydride (ASA), forms a hydrolysis reaction product with multivalentcations, and with calcium in particular. Solubilization of calcium fromPCC or GCC at slightly lower pH conditions in the ion exchange mediumand subsequent removal of the solubilized calcium and/or removal ofbackground dissolved calcium can inhibit or prevent the ASAhydrolyzation reaction. The reaction by-product is very sticky and foulspaper making felts, shower nozzles, and other machinery. Currentlychemical additives such as aluminum compounds are deployed to mitigatethe ASA hydrolyzation reaction with calcium. Elimination of the calciumcan significantly reduce the need for aluminum compounds and increasethe performance of the ASA.

Accordingly, in certain embodiments, the liquid input stream that is tobe recovered can be selected such that the liquid input stream comprisescalcium carbonate (e.g., in the form of PCC and/or GCC). In some suchembodiments, the pH of the stream entering the ion exchange treatmentstep can be adjusted to or maintained at a pH at or below about 7.5, ator below about 7.2, or at or below about 7.1 (and/or, in certainembodiments, substantially below neutral, for example 5.5) during and/orprior to removing at least a portion of the cations using the ionexchange medium. In some such embodiments, adjusting or maintaining thepH of the liquid input stream comprises allowing the liquid input streamto contact the ion exchange medium, and allowing the operating pH of theion exchange medium to reduce the pH of the liquid input stream (e.g.,by using an acidic ion exchange medium, such as a WAC resin). In certainembodiments, allowing the lower operating pH of the ion exchange mediumto reduce the pH of the feed stream can cause the calcium carbonate todissolve and allow the ion exchange medium to take up the free calciumions.

For example, in certain embodiments, the ion exchange medium can beconfigured to remove at least a portion of the ions from the liquidinput stream (e.g., stream 105 in FIG. 1A), and, in some suchembodiments, the recovery method comprises adjusting or maintaining thepH of the liquid input stream at or below about 7.5 (or at or belowabout 7.2, or at or below about 7.1, and/or, in certain embodiments, aslow as, for example 5.5) such that at least a portion of the calciumcarbonate is dissolved in the liquid input stream during and/or prior toremoving at least a portion of the cations from the filtrate streamusing the ion exchange medium. In some embodiments, the ion exchangemedium can be configured to remove at least a portion of the ions from asupernatant stream (e.g., stream 215 in FIG. 2A, described in moredetail below), and, in some such embodiments, the recovery methodcomprises adjusting or maintaining the pH of the supernatant stream ator below about 7.5 (or at or below about 7.2, or at or below about 7.1,and/or, in certain embodiments, substantially below neutral, for example5.5) during and/or prior to removing at least a portion of the cationsfrom the supernatant stream using the ion exchange medium. In certainembodiments, the ion exchange medium can be configured to remove atleast a portion of the ions from a filtrate stream (e.g., stream 330 inFIG. 3, described in more detail below), and, in some such embodiments,the recovery method comprises adjusting or maintaining the pH of thefiltrate stream at or below about 7.5 (or at or below about 7.2, or ator below about 7.1, and/or, in certain embodiments, substantially belowneutral, for example 5.5) during and/or prior to removing at least aportion of the cations from the filtrate stream using the ion exchangemedium. In any one or more of these embodiments, the pH of the inputstream can be maintained or lowered by the ion exchange medium once theinput stream has contacted the ion exchange medium, which can cause thecalcium carbonate to dissolve and allow the ion exchange medium to takeup the free calcium ions.

In addition to removing sparingly soluble ions from whitewater, thewhitewater treatment systems described herein can also make use ofvarious systems (including flocculation-based systems) to removesuspended solids and reduce the level of anionic colloidal material(i.e., anionic trash) within the whitewater stream. Anionic trashreduces the effectiveness of the paper dewatering process. This canresult in an increased amount of steam/energy consumption at the dryersection of the paper machine when forced to dry a poorly dewatered papersheet. In addition, limiting the amount of anionic trash within thewhitewater reduces the overall chemical consumption of the whitewaterrecovery process. Specialized chemical additives (such as polyacrylamideand more common aluminum compounds) are often required to offset thepresence of anionic colloidal trash. Anionic trash can reduce thereactivity with these specialized chemicals, making a portion of thechemical unavailable to react with the fibers. Thus, the specialtychemicals must often be added in excess. By controlling the anionictrash levels within the whitewater, the need to add excess specialtychemicals to control the anionic trash concentration is reduced. It wasunexpectedly discovered that the use of flocculation prior to ionexchange can significantly reduce the amount of colloidal anionicparticles within the whitewater.

The removal of solids and anionic trash can also enhance the degree towhich the ion exchange process is able to remove multivalent ions fromthe whitewater. When ion exchange resins are employed, the ion exchangeresin can act as a filter. If suspended solids are present they can beretained by the ion exchange resin (e.g., within the bed, if locatedwithin a packed column). Suspended solids trapped by the resin bed tendto accumulate at the interface between the ion exchange bed and the feedwater entering the ion exchange column. Very fine solids can alsopenetrate into the ion exchange bead. The use of a cationic ion exchangeresin (i.e., a resin that contains anions such that it is able toattract cations) diminishes the potential for fine solids penetrationinto the interstices of the resin as most of the fine particle have ananion charge and therefore repelled by the cationic resin. Solidsaccumulation in the ion exchange medium (e.g., in the ion exchangecolumn and/or in and around distributors and other piping) results in anincrease in the differential pressure in the ion exchange column,primarily resulting from clogging of the ion exchange resin and thewater distribution and collection system inside the column. Theincreased differential pressure across the ion exchange bed can forcethe water to take the path of least resistance, circumventing the resinbed and traveling down the sides of the ion exchange column in achanneling fashion and thus avoiding intimate contact with the ionexchange resin. To operate most effectively, the ion exchange columnshould operate, in many instances, on a plug flow basis. If the fluid tobe recovered does not receive proper intimate contact with the resin,the resin may be unable to effectively remove the dissolvedcontaminants.

Fine suspended solids can also clog the ion exchange resin. Mineral acidis commonly used to regenerate the resin for removal of contaminants.Suspended solids can block the passage of the chemical, preventingeffective regeneration of the resin and reducing the proper removal ofcontaminants during the contaminant stripping process (regeneration).

FIG. 2A is a schematic illustration of a system 200 in which aflocculation step is performed, along with an ion exchange step, torecover a whitewater stream. In FIG. 2A, liquid input stream 205, whichcomprises whitewater or is derived from whitewater and which containscations and suspended solids, is exposed to a flocculent and, optionallyin certain embodiments, a magnetically responsive material. Uponexposing the whitewater to the flocculent and in certain embodiments themagnetically responsive material, the suspended solids within thewhitewater can interact with the flocculent and in certain embodimentsthe magnetically responsive material to form agglomerations offlocculent, including the magnetically responsive material in thoseembodiments employing magnetically responsive materials, and suspendedsolids, which can be removed. In certain embodiments, after theagglomerations have been formed, at least a portion of theagglomerations can be removed from the whitewater (e.g., using a magnetfor embodiments employing magnetically responsive materials or any othersuitable agglomeration removal apparatus such as a skimmer asappropriate for other embodiments) to produce a supernatant stream 215containing less suspended solids than the liquid input stream 205. Inembodiments in which magnets/magnetically responsive materials areemployed, the magnet can be positioned within the flocculation vessel orwithin a separate vessel specifically dedicated to performing themagnetic separation step. In certain embodiments, one or more magnetsand/or other agglomeration removal devices may be positioned such thatthey are at least partially submerged in the whitewater. In embodimentsin which magnetically responsive material is employed, the presence ofthe magnetically responsive material within the agglomerations withinthe whitewater can cause agglomerations to be attracted to, andeventually stick to, the magnets. Subsequently, the agglomerations canbe removed from the magnets, leaving purified whitewater behind.

A variety of types of flocculent can be used to form agglomerations withsuspended solids. In certain embodiments, the flocculent comprises apolymeric flocculent. For example, the flocculent may be apolyacrylamide-based flocculent, in certain embodiments. In someembodiments, the flocculent comprises a polydiallyldimethylammoniumchloride-based flocculent. Specific examples of polymeric flocculentssuitable for use in the flocculation step include, but are not limitedto, FLOPAM™ EM 140 CT, FLOPAM™ EM 240 CT, FLOPAM™ EM 340 CT, FLOPAM™ EM340 BD, and FLOQUAT™ FL 4440. In certain embodiments, the flocculent canbe non-polymeric. For example, in some embodiments, the flocculentcomprises alum, aluminum chlorohydrate, aluminum sulfate, calcium oxide,calcium hydroxide, iron(II) sulfate, iron(III) chloride, sodiumaluminate, and/or sodium silicate.

In embodiments in which the flocculation step comprises a magnetic-basedflocculation step, a variety of types of magnetically responsivematerial can be used to form agglomerations with the suspended solids.Generally, the phrase “magnetically responsive material,” as usedherein, refers to any material capable of moving through an aqueousmedium upon exposure of the material to a magnetic field. In certainembodiments, the magnetically responsive material is an iron-containingmaterial, including materials containing elemental iron, oxides of iron,or any other iron-containing material. For example, the magneticallyresponsive material comprises magnetite (Fe₃O₄), in some embodiments. Incertain embodiments, the magnetically responsive material is in the formof particles. The magnetically responsive particles can have anysuitable average diameter that allows for easy integration into thewhitewater recovery process (e.g., millimeter-scale diameters orsmaller, in certain embodiments).

In embodiments comprising a magnetic-based flocculation step, a varietyof types of magnets can be used to magnetically manipulate theagglomerations within the flocculation vessel. In certain embodiments,the magnet can be a permanent magnet, including but not limited tomagnets comprising iron, nickel, cobalt, rare earth metals (including,for example, neodymium, praseodymium, samarium, gadolinium, anddysprosium), naturally occurring minerals (including, for example,lodestone), and/or alloys or other mixtures of these. In someembodiments, non-permanent magnets, such as electromagnets, may be used.

In FIG. 2A, liquid input stream 205 is exposed to the flocculent (andoptional magnetically responsive material) within flocculation vessel210. The use of a flocculation vessel is not required, and in otherembodiments, whitewater can be exposed to flocculent (and optionalmagnetically responsive material) outside a vessel. In otherembodiments, multiple flocculation vessels or stages may be employed.

FIG. 2B is a schematic illustration of an exemplary flocculation vessel210, which can be used in association with certain embodiments describedherein in which a magnetic-based flocculation step is performed. In FIG.2B, flocculation vessel 210 comprises flocculation compartment 250, intowhich a magnetically responsive material, the whitewater, and theflocculent can be flowed. Upon flowing the magnetically responsivematerial, the whitewater, and the flocculent into the flocculationcompartment, optional stirring apparatus 255 can be used to enhance thedegree to which the magnetically responsive material, the whitewater,and the flocculent are mixed and become intimately contacted. After themagnetically responsive material, the whitewater, and the flocculenthave mixed, suspended solids within the whitewater can formagglomerations with the magnetically responsive material and theflocculent. In certain embodiments, other ballast media can be used. Forexample, fine graded sand could be used as ballast media.

Upon formation of the agglomerations, some of the agglomerations can beseparated from the whitewater using magnets 270. In FIG. 2B, magnets 270comprise rotatable drums, discs, or screens arranged around elongatedshafts, which can be rotated around their longitudinal axes. In otherembodiments, the magnets may have other configurations. In certainembodiments, magnets 270 can be located at or near the input region offlocculation compartment 250 such that they are able to attract andattach to the agglomerations within the whitewater as it is agitated bystirring apparatus 255.

Many or all of the agglomerations that are not captured by magnets 270continue to swirl in the flocculation compartment 250 and are eventuallycaptured for recovery by magnets 270 at a later time. The flow ofwhitewater can force some of the agglomerations to be passed through thesubmerged weir in the direction of magnetic discs 280. The particles arehowever primarily forced to flow back into flocculation compartment 250because magnetite is over five times denser than water. The relativelyhigh density of the magnetite can greatly enhance the rate at which theagglomerations settle, allowing for much smaller flocculation vesselvolumes (in certain embodiments, between 5 to 20 times smaller thantraditional flocculation units sizes to purify a similar flow rate ofwater).

The agglomerations that are captured by magnets 270 can be scraped fromthe magnets using scraper 275 and subsequently transported back toflocculation compartment 250 once the dirt particles are removed usingsheering discs 278.

Upon removing the agglomerations from the magnets, the magneticallyresponsive material can be mechanically detached from the suspendedsolids using a deagglomeration system. For example, in FIG. 2B, asagglomerations accumulate in agglomeration compartment 250, shearingdiscs 278 can be used to mechanically shear the agglomerations. As theagglomerations are sheared, the magnetically responsive material andwater can be separated from the flocculent and the suspended solids.Suitable deagglomerators that can be used include, but are not limitedto, Delumper® crushers available from Franklin Miller®, Livingston, N.J.and Silverson in-line mixers available from Silverson Machines,headquartered in Waterside, Chesham, United Kingdom.

After being separated using the shearing disc, the magneticallyresponsive material can be picked up using, for example, a magnet.Subsequently, the magnetically responsive material can be reused.

Fine flocculent and suspended solids that escape the retaining submergedweir are captured on magnetic discs 280 and can be scraped off andcollected from a receiving trough 282 and returned to the flocculationchamber, after which the magnetically responsive material is recoveredas described previously. Dirt particles and some polymer separated fromthe magnetically responsive material can be transferred to a solidsdewatering system for removal of the solids using, for example, a beltpress, a filter press, or other similar dewatering device. The resultingcake containing the suspended solids can be burned to provide energy tothe process or discarded. The filtrate from the dewatering device can berecycled back to the flocculation vessel in certain embodiments, orfurther processed.

While the use of a magnetic-based flocculation step has been highlightedabove, it should be understood that the flocculation step does notnecessarily involve the use of magnets and/or magnetically responsivematerial, and in certain embodiments, non-magnetic-based flocculationmay be performed. For example, in some embodiments, the flocculationstep in system 200 of FIG. 2A comprises or includes a non-magneticflocculation step, such as a flocculation step in which sand or othernon-magnetic materials are used as the ballast. In one such set ofembodiments, flocculation vessel 210 comprises a gas input configured toinject gas into fluid contained within flocculation vessel 210. Duringthe flocculation step, gas can be introduced into the whitewater inputstream. The gas can be dissolved in the whitewater under pressure andsubsequently released at atmospheric pressure in a tank or basin, whichcan lead to the formation of gas bubbles. In some such cases,agglomerations adhere to the boundaries of the gas bubbles formed withinthe whitewater such that the agglomerations rise to the top of thewhitewater as the gas bubbles rise. In certain such embodiments,flocculation vessel 210 comprises a dissolved gas flotation separationapparatus, such as a dissolved air flotation separation apparatus.Examples of suitable dissolved air flotation apparatus include, forexample, the PPM® DAF Clarifier and the Saturn™ DAF Clarifiermanufactured by Poseidon (Outremont, Québec, Canada), and the Krofta DAFrecovery system by Ecolab (St. Paul, Minn.). Examples of other suitabledissolved gas flotation apparatus include, for example, the DissolvedGas Flotation (DGF) system, the Cyclosep™ flotation system, theHydrocell® induced gas flotation separator, and the VORSEP™ compactflotation unit, available from Siemens Water Technologies (Broussard,La.).

In certain embodiments, flocculation vessel 210 is configured to allowat least a portion of the agglomerations of flocculent and suspendedsolids to settle to the bottom of the vessel. In such embodiments, theagglomerations can be separated from the whitewater by gravity settlingat least a portion of the agglomerations, and scraping or otherwiseremoving the settled solids from the bottom of the vessel. In some suchembodiments, flocculation vessel 210 comprises a gravity settlingclarifier. Suitable devices for performing various of the flocculationmethods described herein include, but are not limited to, Reactivator®clarifiers available from Graver Water Systems, Inc. (Cranford, N.J.);circular clarifiers and industrial wastewater clarifiers available fromMonroe Environmental Corporation (Monroe, Mich.); and RapiSand™ballasted flocculation systems from WesTech (Salt Lake City, Utah).

In some embodiments, a combination of magnetic-based andnon-magnetic-based flocculation steps can be performed.

In certain embodiments, the flocculation system is capable of recoveringa purified water stream that includes at least 90%, at least 95%, or atleast 98% of the whitewater that enters the flocculation vessel (e.g.,from stream 205) while removing at least 70%, at least 90%, at least95%, or at least 98% of the suspended solids from the whitewater thatenters the flocculation vessel.

In certain embodiments, after at least a portion of the suspended solidshave been removed from the whitewater stream within the flocculationvessel, the processed whitewater can be further processed using an ionexchange medium. For example, in FIG. 2A, supernatant stream 215 isflowed through ion exchange vessel 110. Upon flowing supernatant stream215 through ion exchange vessel 110, at least a portion of the cationscan be removed from the supernatant stream using an ion exchange medium.Removing at least a portion of the cations from supernatant stream 215can produce an ion exchanged effluent stream 225.

The ion exchange medium used in the ion exchange step of FIG. 2A can besimilar to the ion exchange medium described above with respect to FIG.1A. For example, in certain embodiments, the ion exchange mediumcomprises a weak acid cation resin or a strong acid cation resin.Moreover, the configuration of the equipment used to perform the ionexchange step in FIG. 2A can be similar to the configurations of the ionexchange step shown in FIG. 1A. For example, in certain embodiments, atleast a portion of supernatant stream 215 can be flowed through an ionexchange vessel 110 containing the ion exchange medium. The ion exchangevessel comprises, in some embodiments, a packed column. As noted above,the use of an ion exchange vessel is not required, and in otherembodiments, the supernatant stream 215 can be exposed to ion exchangemedium outside a vessel.

Operation of the ion exchange medium exposure step in FIG. 2A can besimilar to that of the ion exchange step described with respect to FIG.1A. For example, the ion exchange medium in ion exchange vessel 110 inFIG. 2A can be used to remove a large percentage of the cations (e.g.,multivalent cations such as any one or more of Mg²⁺, Ca²⁺, Sr²⁺, Ba²⁺,Fe²⁺, Mn²⁺, and/or Al³⁺) to a relatively large degree (e.g., such thatthe amount of cations within ion exchanged effluent stream 225 is atleast about 70% lower, at least about 80% lower, at least about 90%lower, at least about 95% lower, or at least about 99% lower than theamount of cations within stream 215). In some embodiments, the step ofremoving at least a portion of the cations from supernatant stream 215using an ion exchange medium is performed at a pH of between about 4.5and about 6.5. In certain embodiments, the ion exchange step and/or theflocculation step can be combined with additional processing steps toenhance the degree to which suspended solids and/or ions are removedfrom the whitewater. FIG. 3 is a schematic diagram illustrating anexemplary whitewater recovery system 300 including such additionalcomponents. System 300 is configured to process liquid input stream 305,which can contain whitewater or be derived from whitewater. Liquid inputstream 305 can contain suspended solids, such as wood fiber, pulp,colloidal material (including, potentially, anionic colloidal trash),and the like. In certain embodiments, liquid input stream 305 containsanions and/or cations (e.g., multivalent cations such as any one or moreof Mg²⁺, Ca²⁺, Sr²⁺, Ba²⁺, Fe²⁺, Mn²⁺, and/or Al³⁺).

In FIG. 3, liquid input stream 305, comprising whitewater or derivedfrom whitewater, can be exposed to a flocculent. The flocculent can beconfigured to agglomerate with the suspended solids within thewhitewater upon exposure of the flocculent to the whitewater.Accordingly, when liquid input stream 305 is exposed to the flocculent,agglomerations of flocculent and suspended solids can be formed. Incertain embodiments, the flocculent exposure step can be carried out ina flocculation vessel 310, which can contain the flocculent and can beconfigured to accept an input flow of the whitewater (e.g., through oneor more inlets). The flocculation step can be configured to produce asupernatant stream 315 comprising purified liquid containing a lowerquantity of suspended solids than liquid input stream 305, for example,by removing at least a portion of the agglomerations of flocculent andsuspended solids from liquid input stream 305.

In certain embodiments, the flocculation step in FIG. 3 comprises amagnetic-based flocculation step, such as the magnetic-basedflocculation step described in association with FIG. 2A. In such cases,the flocculation vessel can contain magnetically responsive materialconfigured to form agglomerations with the flocculent and the suspendedsolids. In embodiments in which a magnetic-based flocculation step isemployed, the flocculation step can be configured in any of the waysdescribed above with respect to FIG. 2A (e.g., using a magnet toseparate the agglomerations of suspended solids, flocculent, andmagnetically responsive material from the whitewater). In addition, themagnetically responsive material used in such a step can correspond toany of the magnetically responsive materials (e.g., magnetite) describedabove with respect to FIG. 2A.

In some embodiments, the flocculation step in system 300 of FIG. 3comprises or includes a non-magnetic-based flocculation step, includingany of the non-magnetic-based flocculation steps described above inassociation with FIG. 2A. In some embodiments, a combination ofmagnetic-based and non-magnetic-based flocculation steps can beperformed.

System 300 can further comprise a filter 320 configured to receive atleast a portion of supernatant stream 315. Filter 320 can be configuredto filter supernatant stream 315 to produce a retentate stream 325 and afiltrate stream 330. Filter 320 comprises, according to certainembodiments, a porous medium through which supernatant stream 315 can beflowed, leaving behind suspended solids (which can form part of and/orsubsequently be transported away as retentate stream 325) and producingfiltrate stream 330 on the other side of the porous medium. In suchembodiments, filtrate stream 330 generally contains a lower quantity ofsuspended solids than the retentate stream.

A variety of devices are suitable for use as filter 320. Filter 320comprises, in certain embodiments, a plurality of discs stacked on topof each other, and oriented horizontally or vertically. Optionally, thediscs can be rotated during filtration. Water can be transported throughthe discs, leaving suspended solids behind. In certain embodiments, apressure gradient can be applied across the discs, enhancing separation.In certain embodiments, filter 320 comprises a disc filter such as thePetax™ disc filter, manufactured by Kadant, Inc. (Westford, Mass.)

In some embodiments, filter 320 comprises a screen filter. Generally,screen filters include a mesh, perforated material, fabric, or otherfiltration element. In certain such embodiments, a pressurized screenfilter can be used. When pressurized screen filters are employed, duringfiltration, fluid may be pressurized and fed through the filtrationelement. Optionally, after a predetermined pressure drop is establishedacross the filtration element, a backwashing sequence can be initiatedto clean the filtration element. Examples of suitable screen filtersinclude, but are not limited to, the MegaFlow™, Pulse Purge™, and ErGo™pressurized screen filter systems from Kadant, Inc.

Filter 320 comprises, in certain embodiments, a strainer. For example,filter 320 can comprise a gravity strainer. In such strainers,whitewater can be transported through a mesh, perforated material,fabric, or other filtration element using gravity as a driving force.Examples of suitable gravity strainers include Kadant gravity strainermodels GS 4005, GS 4015, GS 4025, GS 4035, and GS 4045. In certainembodiments, a vacuum assisted gravity strainer can be employed, such asKadant models VA 05, VA 15, VA 25, VA 35, and VA 45. In vacuum assistedgravity strainers, a vacuum is applied to the filtrate side of thefiltration element, which enhances the rate at which fluid is drawnthrough the filtration element.

In certain embodiments, filter 320 comprises a depth filtration medium,such as sand (e.g., in the form of graded layers of sand gravel) and/orother filter media. The whitewater can be transported from a first sideof the depth filtration medium to a second side of the depth filtrationmedium, leaving behind suspended solids within the bulk of thefiltration medium, and producing purified whitewater on the second sideof the filtration medium.

The suspended solids captured by filter 320 can be removed from thefilter via retentate stream 325. Filter 320 can be configured, in someembodiments, such that at least a portion 328 of retentate stream 325 isrecycled to flocculation vessel 310. This can be achieved, for example,by flowing a stream of water (e.g., via stream 322) through the filterto remove the retained solids, and subsequently transporting at least apart of the resulting suspension (e.g., all or part of the liquidportion of the suspension) to the flocculation vessel. In some suchembodiments, portion 328 of the retentate portion of the processedwhitewater is used to form a suspension of agglomerations withinflocculation vessel 310. By using filter 320 to capture suspended solidsin this way, the transportation of the suspended solids to downstreamoperations (e.g., ion exchangers, dissolved solids removal apparatus,etc.)—which can become clogged or are otherwise sensitive to thepresence of suspended solids—can be prevented.

In certain embodiments, system 300 comprises an ion exchange vessel 335configured to receive at least a portion of filtrate stream 330. Ionexchange vessel 335 can contain an ion exchange medium configured toremove at least a portion of the cations (e.g., multivalent cations suchas Mg²⁺, Ca²⁺, Sr²⁺, Ba²⁺, Fe²⁺, Mn²⁺, and/or Al³⁺) from filtrate stream330 to produce ion exchanged effluent stream 340. The multivalent ionscan be removed from the ion exchange medium (e.g., using any of the ionexchange medium regeneration steps described elsewhere) via stream 338.

The ion exchange medium used in the ion exchange step of FIG. 3 can besimilar to the ion exchange medium described above with respect to FIGS.1A and 2A. For example, in certain embodiments, the ion exchange mediumcomprises a weak acid cation resin or a strong acid cation resin.Moreover, the configuration of the equipment used to perform the ionexchange step in system 300 can be similar to the configurations of theion exchange steps illustrated in FIGS. 1A and 2A. For example, incertain embodiments, ion exchange vessel 335 can be in the form of apacked bed, through which at least a portion of filtrate stream 330 canbe flowed to remove cations from the filtrate stream. As notedelsewhere, the use of an ion exchange vessel is not required, and inother embodiments, filtrate stream 330 can be exposed to ion exchangemedium outside a vessel. Finally, operation of the ion exchange step inFIG. 3 can be similar to that of the ion exchange steps described withrespect to FIGS. 1A and 2A. For example, the ion exchange medium in ionexchange vessel 335 in FIG. 3 can be used to remove a large percentageof the cations (e.g., multivalent cations such as any one or more ofMg²⁺, Ca²⁺, Sr²⁺, Ba²⁺, Fe²⁺, Mn²⁺, and/or Al³⁺) to a relatively largedegree (e.g., such that the amount of cations within ion exchangedeffluent stream 340 is at least about 70% lower, at least about 80%lower, at least about 90% lower, at least about 95% lower, or at leastabout 99% lower than the amount of cations within filtrate stream 330).In some embodiments, the step of removing at least a portion of thecations from filtrate stream 330 using an ion exchange medium isperformed at a pH of between about 5.5 and about 8.5.

System 300 further comprises, in certain embodiments, optional totaldissolved solids removal apparatus 345. Total dissolved solids removalapparatus 345 can be configured to receive at least a portion of theprocessed whitewater contained within ion exchange vessel 335. Apparatus345 is generally configured to reduce the amount of total dissolvedsolids within stream 340. For example, when stream 340 is transportedthrough total dissolved solids removal apparatus 345, at least a portionof the total dissolved solids within stream 340 (i.e., the dissolvedsolids remaining in the processed whitewater after the ion exchange stephas been performed) can be removed to produce stream 350, which containsdissolved solids in amount less than the amount in stream 340. Incertain embodiments, total dissolved solids removal apparatus 345 isconfigured to remove anions from stream 340 such that the amount ofanions within stream 350 is lower than the amount of anions withinstream 340.

A variety of apparatus are suitable for use in removing dissolved solidsfrom stream 340. In certain embodiments, total dissolved solids removalapparatus 345 is configured to perform reverse osmosis. Reverse osmosisis a membrane-based filtration method in which large molecules and ionscan be removed from solution by applying pressure to the solution whenit is on one side of a selective membrane, resulting in solute(containing the ions/molecules) being retained on the pressurized sideof the membrane and solvent passing through the membrane. Suitablemembranes for use in reverse osmosis apparatuses include, but are notlimited to, those available from Dow Chemical Company's Filmtec Divisionin Midland, Mich. (e.g., BW 30-400/44 I, BW-30-400i, LE-400, andSW-400-FR) and those available from Koch Membranes in Wilmington, Mass.(e.g., TFC-HR 8 inch, TFC HF MegaMagnum, and TFC-SW MegaMagnum). Incertain embodiments, the reverse osmosis unit can be operated atrelatively high temperatures (e.g., greater than 110° F.), to facilitaterecovery of the heat energy in the whitewater. The application of heatcan reduce the rejection of dissolved solids while allowing the reverseosmosis unit to operate at a higher flux.

In some embodiments, total dissolved solids removal apparatus 345 isconfigured to perform nanofiltration. Nanofiltration generally refers toa process in which a relatively low amount of pressure (e.g., up to 3MPa) is used to transport fluid through a membrane comprising nanoscalepores (e.g., pores with diameters of 100 nanometers or less, often withdiameters of around 1 nanometer). Generally, nanofiltration uses smallerpressures and membranes with larger pore sizes compared to those used inreverse osmosis process. Suitable membranes for use in nanofiltrationapparatuses include, but are not limited to, those available from DowChemical Company's Filmtec Division in Midland, Mich. (e.g., NF90-400and NF270-400) and those available from Koch Membranes in Wilmington,Mass. (e.g., TFC-SR 100-330 and TFC SR-400).

In certain embodiments, total dissolved solids removal apparatus 345 isconfigured to perform a second ion exchange process. The second ionexchange process can be configured to remove anions from the whitewater.The second ion exchange process can be fabricated by immobilizing an ionexchange medium within a vessel, for example, in the form of a packedcolumn. One of ordinary skill in the art, given the present disclosure,would be capable of selecting an appropriate ion exchange resin forremoval of a particular anion from a whitewater stream. Examples of ionsthat can be removed from the whitewater include, but are not limited to,Cl⁻, SO₄ ²⁻, NO₃ ⁻, PO₄ ⁻³, SiO₂, CO₂, and OH⁻. Examples of ion exchangemedia that could be used to remove such ions include, but are notlimited to, MP 64, MP 62, M-504, and MP 600 (available from Bayer'sLanxess division in Pittsburgh, Pa.) and SBR-P, MWA-1, and IRA 910(available from Dow Chemical Company in Midland, Mich.).

Generally, total dissolved solids removal apparatus 345 is positioneddownstream of the flocculation, filtration, and ion exchange units. Bypositioning the total dissolved solids removal apparatus downstream ofthese units, one can ensure that suspended solids (including anioniccolloidal trash and suspended organic material) and ions that causescaling—both of which can plug and foul the components of the totaldissolved solids removal apparatus—are removed from the whitewater priorto the whitewater being transported through the total dissolved solidsremoval apparatus. Such upstream removal of suspended solids and scalecausing ions can dramatically reduce component fouling and the need forcomponent cleaning, and can lead to high water recovery rates for thetotal dissolved solids removal system.

In certain embodiments, a stream of water can be used to transport thesolids and ions captured by the total dissolved solids removal apparatusaway from the apparatus, for example, via stream 348 in FIG. 3. Becausethe water within stream 348 is low in suspended solids and scale formingions, this stream can be recycled directly to certain parts of thepapermaking process without the need for further purification. Forexample, warm dissolved solids removal apparatus reject water can beused for flushing systems at the paper or pulp mill. In someembodiments, stream 348 can be introduced to a second total dissolvedsolids removal apparatus stage (e.g., a second reverse osmosis unit, orother suitable unit) for further purification. Incorporating additionaltotal dissolved solids removal apparatuses would increase the overallrecovery rate of the combined units.

In certain embodiments, system 300 comprises optional electromagneticradiation exposure system 355. Electromagnetic radiation exposure system355 can be configured to expose recovered whitewater from the ionexchange vessel to electromagnetic radiation. While electromagneticradiation exposure system 355 is illustrated in FIG. 3 as receivingfluid directly from dissolved solids removal apparatus 345, in otherembodiments, the order of electromagnetic radiation exposure system 355and total dissolved solids removal apparatus 345 may be switched, and instill other embodiments, total dissolved solids removal apparatus 345may not be present at all. That is to say, in certain embodiments,electromagnetic radiation exposure system 355 can be configured toreceive a liquid stream directly from ion exchange vessel 335 ordirectly from dissolved solids removal apparatus 345.

Electromagnetic radiation exposure system 355 can be configured toexpose the liquid within stream 350 to at least one wavelength ofultraviolet electromagnetic radiation (e.g., electromagnetic radiationwith a wavelength of from about 10 nm to about 400 nm), in certainembodiments. The whitewater in a process stream can be exposed toelectromagnetic radiation, for example, by including a region in theconduit through which the whitewater is transported that is transparentto the wavelength(s) of electromagnetic radiation that are to be used toprocess the whitewater. For example, an optical window that istransparent to, for example, ultraviolet electromagnetic radiation canbe included in a conduit through which white water is transported.

In some embodiments, electromagnetic radiation exposure system 355sterilizes or reduces the bio burden of the whitewater. As oneparticular example, ultraviolet electromagnetic radiation can be used todestroy DNA, kill or otherwise render bacteria non-viable, or otherwisesterilize the whitewater within stream 350. In certain embodiments,electromagnetic radiation exposure system 355 comprises one or moreamalgam ultraviolet lamps, such as those manufactured by HeraeusNoblelight GmbH, Hanau, Germany. The use of electromagnetic radiation tocontrol bacteria and slime may allow for significantly reduced use ofbiocides and slimacides—some of which are poisonous—in the whitewaterloop(s). The electromagnetic radiation exposure step can be locateddownstream of the ion exchange process and/or the total dissolved solidsremoval apparatus (and, in certain embodiments, at the end of thewhitewater recovery process) in order to facilitate the most efficienttransmittance of electromagnetic radiation (and especially ultravioletelectromagnetic radiation) through a processed whitewater stream.

In some embodiments, recovery heat exchangers can be placed at variouslocations within the system. The recovery heat exchangers may be used toremove heat from the whitewater and/or processed whitewater andsubsequently pre-heat input streams (such as fresh make-up waterstreams) to appropriate temperatures. The use of recovery heatexchangers can reduce the total amount of energy required to operate thewater recovery system.

FIGS. 4A-4C are schematic illustrations of another exemplary system thatcan be used to remove suspended solids and multivalent ions fromwhitewater. In FIG. 4A, whitewater stream 401 is mixed with polymerflocculant within stream 402 and transported to tank 403. Upon mixingthe whitewater stream with the flocculant, the mixture is transportedout of tank 403 via stream 404. In certain cases, a portion of stream404 is recycled back to tank 403 via stream 404B. The whitewater andflocculant mixture within stream 404 is transported to an optionalmagnetic ballast tank 406, where suspended solids are removed. Optionalmagnetic ballast tank 406 can be configured in a similar manner as thesystem illustrated in FIG. 2B. Water within stream 407 can betransported to optional magnetic ballast tank 406 to assist in captureof the magnetically responsive ballast material on magnets 408. Incertain embodiments, non-magnetic-based flocculation steps (e.g., usingany of the processes or equipment described elsewhere herein) can beperformed in addition to or in place of the magnetic-based flocculationstep illustrated in FIG. 4A.

Processed water from tank 406 can be captured in trough 409 andsubsequently transferred to collection tank 411 via stream 410. Sludgeproduced during the suspended solids removal step within tank 406 can betransported to sludge tank 414 via streams 451. The sludge within tank414 can be removed via stream 450 and subsequently dewatered and/ordisposed of.

The contents of tank 411 can be transported via stream 412 to discfilter 413. In certain cases, a portion of stream 412 can be transportedto sludge tank 414 (e.g., via stream 412B). Vacuum pumps can be used todraw a vacuum on the filters within disc filter 413, producing filtratestream 418, which can be subsequently transported to collection tank 421for further processing.

The system can include a disk washing apparatus 415, which can beconfigured to transport rinsing agents over the filters within discfilter 413. For example, rinsing agents can be pumped via stream 415Ainto disc filter 413. Vacuum pumps 417 can subsequently be used to drawthe solids to the filter media and spray showers can be used to removethe accumulated cake solids. Effluent from the disk washing process canbe transported out of the system, for example, into sludge tank 414(e.g., via stream 416) or into collection tank 421 (e.g., via stream420), optionally first being filtered using filter 419.

As noted above, the contents of collection tank 421 can be furtherprocessed to remove other contaminants from the whitewater. For example,a portion of the contents of tank 421 can be transported via stream 423to tank 406 and/or tank 411 for further processing. A portion of thecontents of tank 421 can be transported via stream 422 to an ionexchange process. FIG. 4B is a schematic illustration outlining the ionexchange processing of whitewater within stream 422. In FIG. 4B, thecontents of stream 422 can be transported to optional cartridge filter427, which can be used to remove residual suspended solids that remainwithin stream 422 and guard against upsets from the disc filter toproduce cartridge filter effluent stream 426A. In certain cases, some orall of the contents of stream 422 can bypass cartridge filter 427 viastream 426B, for example, for maintenance. In embodiments in which acartridge filters employed, the effluent from the cartridge filter andor the bypass stream can be transported to an ion exchange column 429via stream 428. Ion exchange column 429 can be packed with an ionexchange resin, which can be used to substitute multivalent ions withinstream 428 with monovalent ions from the ion exchange medium. After theion exchange process has been completed, the processed water to betransported via stream 442 to effluent tank 443. Subsequently, thecontents of tank 443 can be transported out of tank 443 via stream 444.In some cases, a portion of the contents of stream 444 can betransported back to the paper making process via stream 445.

The ion exchange column can be regenerated, for example, by washing theion exchange medium with acidic and alkaline solutions. For example, inFIG. 4B, sulfuric acid within vessel 431A can be pumped via pump 431Band transported to the ion exchange column via stream 430, as part of anion exchange medium regeneration process. In addition, sodium hydroxidesolution or another suitable alkaline solution from vessel 432A can bepumped using pump 432B to ion exchange column 429 via stream 440 as partof an ion exchange medium neutralization process. Optionally, water canbe added to the ion exchange medium during the regeneration process. Forexample, fresh water within stream 446 can be transported through watersoftener 455 and subsequently transported to the ion exchange medium viastream 456. In certain embodiments, a portion of processed whitewaterwithin stream 444 can be transported to the ion exchange medium viastream 456, in addition to or in place of the fresh water from watersoftener 455. Waste water from the ion exchange regeneration process canbe transported to collection tank 470, for example, via stream 462.

In FIG. 4B, stream 459 can be used as a common recirculation line formixing the acid and caustic waste from the ion exchange system. Streams460 and 461 can also be included in the system. In certain embodiments,streams 460 and 461 are part of a tank recirculation system and receiveadditional acid or caustic for neutralization of tank 470 based on thepH of the neutralization tank. Stream 458 can be included, in certainembodiments, as a pressurized drain from discharge tank 470, forexample, to a mill wastewater treatment plant. In some embodiments,streams 457 and 445 can be included, which are system discharges. Insome embodiments, one of stream 457 and 445 can be routed back to themill for reuse and the other can be routed to the optional reverseosmosis system.

The fresh water softening step can be eliminated, for example, incertain embodiments in which hydrochloric acid or similar acid is usedin place of sulfuric acid. This can be preferable in certain embodimentsin which iron is present in the whitewater. In such a system, units 443and 455 and stream 444 could be eliminated, and discharge line 441 couldbe primarily used.

In some embodiments, rather than being directly transferred from ionexchange column 429 to effluent tank 443, at least a portion of thewhitewater within stream 442 can be subjected to a total dissolvedsolids removal step and/or an ultraviolet radiation exposure step (e.g.,by being transported through stream 441), and subsequently transportedto effluent tank 443.

In certain embodiments, an acid/alkaline rinsing arrangement can be usedto regenerate exhausted ion exchange medium. One exemplary process forregenerating the exhausted ion exchange medium is illustrated in FIG.4C. Upon exhaustion of the ion exchange medium within column 429, thecolumn can be removed from service and stand-by ion exchange units canthen be placed in service. Regeneration of the exhausted ion exchangeunit can be performed, for example, by first introducing acid from acidsource 494 (e.g., a dilute mineral acid) in a down flow acidintroduction step. Next, water (e.g., from water source 490) can be usedto displace the acid in a down flow displacement step. The water that isused to displace the acid can be fresh water (e.g., in certainembodiments in which hydrochloric acid is used in the wash step) and/orsoftened water (e.g., in certain embodiments in which sulfuric acid isused in the wash step) can be used. Next, a caustic liquid (e.g., diluteNaOH) from caustic source 492 can be used to rinse (and, for example,neutralize) the column, for example, in an up flow caustic rinse step.Finally, an air mix step can be performed using air from source 496 touniformly distribute resins to establish a near neutral operating pH ofthe ion exchange material and the product water. After regeneration ofthe ion exchange medium, the column can be returned to the process foruse.

Various systems and methods described herein may provide a variety ofadvantages compared to prior art whitewater recovery system. Forexample, the use of flocculation and/or ion exchange processes may allowfor a reduction of scaling through the elimination of multivalentcations that result in precipitation of sparingly soluble salts whencombined with their counter ions (such as sulfate or carbonate) to formscaling precipitates. The use of a flocculation step (e.g., amagnetic-based flocculation step and/or a non-magnetic basedflocculation step, such as dissolved gas flotation or similarsedimentation or flotation clarifier steps) may result in the reductionof the amount of anionic colloidal substances (i.e., anionic trash)within the whitewater. This may allow for a substantial reduction in theuse of chemical additives (which are often employed, for example, forfiber retention but are themselves consumed by the anionic trash) withinthe paper making process. In addition, the use of an ion exchangeprocess for the removal of scale-forming ions may further reduce theneed to add chemical reagents to control scale-forming ions. Removal ofthe scale-forming ions and anionic trash can decrease paper machine drawissues, increase the surface tension of the water used to form the paper(thereby increasing the wet strength of the paper), improve the bondingof paper fibers used in the papermaking process, enhance paper thicknessuniformity, and increase paper brightness.

One particular example of chemical additive reduction relates topapermaking processes in which alkylsuccinic acid anhydride (ASA) isemployed. ASA is used as a sizing agent and is often introduced at thehead box of the paper machine. The presence of Ca²⁺ and othermultivalent cations can cause ASA to rapidly hydrolyze. The hydrolysisproduct of ASA and Ca²⁺ is sticky and can cause fouling of the papermachine, paper products and felts. To minimize the formation of thehydrolysis reaction by-product, control of the concentration of Ca²⁺concentration is important. The current technology for control of theASA hydrolysis reaction by-products is the addition of aluminum salts.Certain embodiments of the inventive systems and methods describedherein, however, can virtually eliminate the need to add aluminum saltsto control the fouling of the ASA hydrolysis byproduct. This results inthe reduction of the amount of aluminum salt added to the system, adecrease in the need for excess ASA addition to compensate forhydrolysis reactions with Ca²⁺ (and enhanced performance of the ASA thatis added), a decrease in fouling from calcium-based scale, and reduceddowntime of the papermaking apparatus for cleaning and maintenance.

Another particular example of chemical additive reduction relates topapermaking processes in which polyamidoamine-epichlorohydrine (PAAE) isemployed. The use of polyamidoamine-epichlorohydrine (PAAE) is common intissue production for increasing wet strength and for its capabilitiesto perform in a broad pH range (5-8) and for the reduction in the use ofcarcinogenic formaldehyde based resins of the past. The amine group as acationic species is able to control adverse effects from the presence ofanionic trash in cycled whitewater. Chemical manufactures suggestconcentrations as high as 1% can be used for the anionic trash control.Dosages of 1% (Based on Dry Fiber) or less does not commonly support wetstrength functionality. Normal wet strength functionality is achieved atPAAE concentrations of 2 to 8% for tissue and corrugated products thatrequire wet strength. Qualitatively, if one considers that ⅛ to ½ of thePAAE is consumed by the anion trash the cost of the PAAE for itsintended function is significantly affected by the presence of aniontrash in a cycled whitewater. Accordingly, reduction or elimination ofanionic trash in the whitewater loops will contribute to a chemical costsavings when using PAAE. Globally, the reduction in the use of PAAE alsoresults in the reduction of some of the adverse by-products from the useof PAAE such as dichloropropanol (DCP) and monodichloropropandiol MCPD).DCP and MCPD are recognized chloro-organic monomers (AOX—AbsorbableOrganic Halide) and are toxic to the environment and thus oftenregulated.

Certain embodiments of the inventive systems and methods can also reduceor eliminate the need for biocides and slimacides, many of which arepoisonous, through the use of electromagnetic radiation-based biologicalmaterial elimination or through the use of ozone.

Certain embodiments of the systems and methods described herein can alsobe used to reduce the amount of fresh water used in common papermakingprocesses that treat and discharge (instead of recycling) whitewater,while producing only a minimal amount of sludge. In addition, heat maybe recovered from various points of the whitewater recovery process,resulting in reduced energy consumption and a corresponding reduction ingreenhouse gas emissions.

Certain embodiments of the inventive whitewater recovery systems andmethods described herein can be integrated with papermaking processes inany suitable fashion. That is to say, the whitewater that is fed to thewhitewater recovery system can originate from any suitable location inthe papermaking process, and the recovered whitewater can bere-introduced to the papermaking process at any suitable location. Incertain embodiments, the whitewater that is to be recovered (e.g.,within stream 105, 205, and/or 305) originates from a paper machine(e.g., the seal pit of a paper machine), a fiber recovery device (e.g.,the clear leg of a fiber recovery device such as a disc filter), or asimilar device or location within a papermaking process. In certainembodiments, the recovered whitewater (e.g., the whitewater withinstream 115, 225, 340, 350, and/or 360) can be distributed to a single ormultiple points within the papermaking process, including the papermachine, the paper machine support systems, and/or the pulp mill forreuse.

In general, it is not practical, nor is it necessary to process the fullflow of the whitewater loops within a typical papermaking process.Rather, it is generally only necessary to process a sufficiently sizedslip stream of the whitewater that includes a sufficient contaminantload for removal to bring the system into equilibrium. Generally, thecontaminant removal rate of the overall whitewater recovery andpurification process should be greater than the contaminant introductionrate within the papermaking process.

The following examples are intended to illustrate certain embodiments ofthe present invention, but do not exemplify the full scope of theinvention.

Example 1

This example describes the use of an ion exchange resin to removemultivalent cations from whitewater samples. A detailed analysis of themill whitewater sample used for the ion exchange testing described inthis example is outlined in Table 1 below.

TABLE 1 Composition of Mill Whitewater Analyzed in Example 1. Equiv.Conv. Amount Formula Amount Wt. Amount Factor mg/L as Species Wt. mg/Lmg/L meq/L (x) CaCO₃ CATIONS Ca(+2) 40.08 48 20.04 2.35 2.50 119.76Mg(+2) 24.31 4.6 12.16 0.38 4.11 18.92 Na(+) 22.99 726 22.99 2.171578.96 K(+) 39.10 25.2 39.10 1.28 32.22 Sr(+2) 87.62 0.13 43.81 0.00301.14 0.15 Ba(+2) 137.33 0.1 68.67 0.0010 0.73 0.07 Al(+3) 26.98 8.995.56 0.00 NH₄(+) 18.04 18.04 2.77 0.00 Cr(+3) 52.00 17.33 2.88 0.00Fe(+2) 55.85 27.93 1.79 0.00 Fe(+3) 55.85 1 18.62 0.0500 2.69 2.69Mn(+2) 54.94 0.23 27.47 0.0080 1.82 0.42 Ni(+2) 58.71 29.36 1.70 0.00Cu(+2) 63.54 31.77 1.57 0.00 Ag(+) 107.87 107.87 0.46 0.00 Zn(+2) 65.3732.69 1.53 0.00 Cd(+2) 112.40 56.20 0.89 0.00 Sn(+2) 118.69 59.35 0.840.00 Pb(+2) 207.19 103.60 0.48 0.00 TOTAL CATIONS: 2.79200 — 1753.19ANIONS HCO₃(−) 61.02 876 61.02 0.82 717.83 CO₃(−2) 60.01 30.00 1.67 0.00SO₄(−2) 96.06 110 48.03 1.04 114.51 Cl(−) 35.45 130 35.45 1.41 183.34NO₃(−) 62.01 2.1 62.01 0.81 1.69 PO₄(−3) 94.97 2.7 31.66 1.58 4.26CrO₄(−2) 115.99 58.00 0.86 0.00 F(−) 19.00 19.00 2.63 0.00 MoO₄(−2)159.94 79.97 0.63 0.00 WO₄(−2) 247.84 123.92 0.40 0.00 B 10.81 10.814.63 0.00 TOTAL ANIONS: — 1021.64 SiO2 60.09 60.1 0.83 TDS ppm NaCl ppmCaCO₃ Conductivity umho/cm or uS/cm COD 4300 OTHER pH 6.5 TemperatureTOC Turbidity TDS TSS 590.00

The species targeted for removal via the ion exchange process werecalcium (Ca²⁺), magnesium (Mg²⁺), strontium (Sr²⁺), barium (Br²⁺), Iron(Fe²⁺), and manganese (Mn²⁺). Aluminum (Al³⁺) was also targeted forremoval, but its concentration was not analyzed during this session oftesting.

Lewatit® CNP80-WS from Lanxess (Leverkusen, Germany), which is a weakacid cation (WAC) resin, was used as the ion exchange resin. Theoperating capacity of the ion exchange resin was determined byconsidering the combined equivalent ionic load from the above-identifiedtarget species, along with the amount of whitewater processed during thetesting. The volume of resin used in the testing was 260 milliliters.The total amount of whitewater that was processed was about 170 liters.The targeted combined ionic load from the target species removed by theion exchange resin during testing was 481 MEQ/mL. Therefore, the targetoperating capacity was 1.85 EQ/L, or 40.4 kilograins/cubic foot ofresin. During testing, the whitewater sample was held at 70° F. Thecapacity for the WAC resin increased with an increase in temperature.The actual field operating temperature for the whitewater at the millfrom which the whitewater was sampled was 122° F. Therefore, it isexpected that the actual capacity realized in the field would be evengreater than that reported in this example.

The whitewater sample was pre-filtered using a 15 micrometer cartridgefilter. The whitewater was transported through the ion exchange resin ata rate of 13 liters/hour (about 50 bed volumes per hour). The test runwas performed for 13 hours. FIGS. 5A, 5B, and 5C are plots of theconcentrations of calcium, magnesium, and manganese, respectively, as afunction of the testing time. The testing demonstrated an operatingcapacity of 1.85 EQ/L. As can be seen from FIGS. 5A-5C, theconcentrations of each of calcium, magnesium, and manganese were greatlyreduced within the first few minutes. In addition, the iron content ofthe whitewater was reduced from 1.04 mg/L to 0.4 mg/L (a 61% reduction);the strontium content was reduced from 0.13 mg/L to less than 0.01 mg/L(a 92% reduction); and the barium content was reduced from 0.099 mg/L to0.007 mg/L (a 93% reduction).

Comparative Example 2

This example describes the use of chemical softening—a strategy commonlyemployed in prior systems—to control ion concentration within awhitewater stream.

Chemical softening is a well-established process used to removemultivalent cations from aqueous streams. In a typical chemicalsoftening process, the pH of the recovered water is raised (e.g., to apH of 10.5, 11, or higher) to decrease the solubility of sparinglysoluble salts (e.g., multivalent cations such as Ca²⁺, Mg²⁺, and thelike). Once the sparingly soluble salts reach their saturation point,they precipitate, and can be removed from the water as sludge in anexternal solids dewatering step.

A 20 gallon sample of whitewater was subjected to a chemical softeningprocess. The chemical properties of the whitewater sample is outlined inTable 2 below.

TABLE 2 Chemical properties of whitewater sample tested in ComparativeExample 2 pH 5.5 TSS 133 mg/l TDS 5880 mg/l Calcium 586 mg/l as CaCO₃Sodium 1440 mg/l as CaCO₃  Magnesium  86 mg/l as CaCO₃ Alkalinity 417mg/l Sulfate 300 mg/l Temperature 140° F.

The goal of the chemical softening process was to reduce total suspendedsolids (TSS) to less than 30 mg/L, reduce the calcium ion concentrationto less than 20 mg/L as CaCO₃, and to reduce the magnesium ionconcentration to less than 20 mg/L as CaCO₃. To achieve these targetremoval end points, 900 mg/L of hydrated lime (Ca(OH)₂) and 1900 mg/L ofsoda ash (Na₂CO₃) were added to the water. The pH of the water was about11 during the processing step.

After addition of the hydrated lime and soda ash, the total suspendedsolids (TSS) were increased to 400 mg/L, the amount of calcium ions inthe water was reduced to 16 mg/L as CaCO₃, and the amount of magnesiumions in the water was reduced to 2.3 mg/L, both below their targetlevels. However, adding the hydrated lime and soda ash to the whitewaterincreased—rather than decreased—the amount of total suspended solidswithin the whitewater. Increasing levels of suspended solids in awhitewater stream would lead to machine fouling upon recycling thewhitewater back to the papermaking process. In addition, the amount oftotal dissolved solids in the recovered stream increased to 4500 mg/L.Increasing TDS concentrations generally increases the solubility of manysparingly soluble salts, which can interfere with the performance of thechemical softener and necessitate a further increase in chemicaladdition. Also increases in TDS results in consumption of drainage aids.This causes a wetter sheet to enter the dryer section and increase steamenergy demand to dry the wetter sheet.

The chemical softening process creates a number of additionalundesirable effects (in addition to the issues associated withincreasing the TDS and TSS levels) during cycles of recovery andconcentration of contaminants in whitewater loops. For example, spacerequirements for chemical softening processes are significantly largerand more costly to implement, relative to the inventive systemsdescribed elsewhere herein. Chemical softening processes generallyrequire a circular solids contact softening clarifier. Based on thetesting, A 3000 gpm whitewater softening clarifier would requireapproximately 910 square feet of a clarifier reaction zone. In additionthe chemical softeners require a number of large and costly supportequipment, including a lime silo for slaked lime, soda ash storage andfeed system, polymer storage and feed systems, and sludge handlingsystems.

Chemical softening process also generally produce large volumes ofsludge with little or no recovery value and discharge significantamounts of salts into the environment.

In addition, large scale clarification systems are normally placedoutside and are open to the atmosphere, which can create heat losses.The heat loss would diminish the potential for recovering and using warm(e.g., 100° F. to 140° F.) whitewater.

Finally, solids contact softening clarifiers are generally used inchemical softening processes. The solids contact softening clarifiersgenerally operate at atmospheric pressures, which results in linepressure loss when the whitewater enters the clarifier. A subsequentre-pressurization pump station is then needed to transport thesupernatant water. The use of a re-pressurization pump station increasesenergy demands for the system and diminishes the potential return oninvestment of the whitewater recycling process.

While several embodiments of the present invention have been describedand illustrated herein, those of ordinary skill in the art will readilyenvision a variety of other means and/or structures for performing thefunctions and/or obtaining the results and/or one or more of theadvantages described herein, and each of such variations and/ormodifications is deemed to be within the scope of the present invention.More generally, those skilled in the art will readily appreciate thatall parameters, dimensions, materials, and configurations describedherein are meant to be exemplary and that the actual parameters,dimensions, materials, and/or configurations will depend upon thespecific application or applications for which the teachings of thepresent invention is/are used. Those skilled in the art will recognize,or be able to ascertain using no more than routine experimentation, manyequivalents to the specific embodiments of the invention describedherein. It is, therefore, to be understood that the foregoingembodiments are presented by way of example only and that, within thescope of the appended claims and equivalents thereto, the invention maybe practiced otherwise than as specifically described and claimed. Thepresent invention is directed to each individual feature, system,article, material, and/or method described herein. In addition, anycombination of two or more such features, systems, articles, materials,and/or methods, if such features, systems, articles, materials, and/ormethods are not mutually inconsistent, is included within the scope ofthe present invention.

The indefinite articles “a” and “an,” as used herein in thespecification and in the claims, unless clearly indicated to thecontrary, should be understood to mean “at least one.”

The phrase “and/or,” as used herein in the specification and in theclaims, should be understood to mean “either or both” of the elements soconjoined, i.e., elements that are conjunctively present in some casesand disjunctively present in other cases. Other elements may optionallybe present other than the elements specifically identified by the“and/or” clause, whether related or unrelated to those elementsspecifically identified unless clearly indicated to the contrary. Thus,as a non-limiting example, a reference to “A and/or B,” when used inconjunction with open-ended language such as “comprising” can refer, inone embodiment, to A without B (optionally including elements other thanB); in another embodiment, to B without A (optionally including elementsother than A); in yet another embodiment, to both A and B (optionallyincluding other elements); etc.

As used herein in the specification and in the claims, “or” should beunderstood to have the same meaning as “and/or” as defined above. Forexample, when separating items in a list, “or” or “and/or” shall beinterpreted as being inclusive, i.e., the inclusion of at least one, butalso including more than one, of a number or list of elements, and,optionally, additional unlisted items. Only terms clearly indicated tothe contrary, such as “only one of” or “exactly one of,” or, when usedin the claims, “consisting of,” will refer to the inclusion of exactlyone element of a number or list of elements. In general, the term “or”as used herein shall only be interpreted as indicating exclusivealternatives (i.e. “one or the other but not both”) when preceded byterms of exclusivity, such as “either,” “one of,” “only one of,” or“exactly one of.” “Consisting essentially of,” when used in the claims,shall have its ordinary meaning as used in the field of patent law.

As used herein in the specification and in the claims, the phrase “atleast one,” in reference to a list of one or more elements, should beunderstood to mean at least one element selected from any one or more ofthe elements in the list of elements, but not necessarily including atleast one of each and every element specifically listed within the listof elements and not excluding any combinations of elements in the listof elements. This definition also allows that elements may optionally bepresent other than the elements specifically identified within the listof elements to which the phrase “at least one” refers, whether relatedor unrelated to those elements specifically identified. Thus, as anon-limiting example, “at least one of A and B” (or, equivalently, “atleast one of A or B,” or, equivalently “at least one of A and/or B”) canrefer, in one embodiment, to at least one, optionally including morethan one, A, with no B present (and optionally including elements otherthan B); in another embodiment, to at least one, optionally includingmore than one, B, with no A present (and optionally including elementsother than A); in yet another embodiment, to at least one, optionallyincluding more than one, A, and at least one, optionally including morethan one, B (and optionally including other elements); etc.

In the claims, as well as in the specification above, all transitionalphrases such as “comprising,” “including,” “carrying,” “having,”“containing,” “involving,” “holding,” and the like are to be understoodto be open-ended, i.e., to mean including but not limited to. Only thetransitional phrases “consisting of” and “consisting essentially of”shall be closed or semi-closed transitional phrases, respectively, asset forth in the United States Patent Office Manual of Patent ExaminingProcedures, Section 2111.03.

What is claimed is:
 1. A system for the recovery of whitewatercontaining cations and suspended solids, comprising: a flocculationvessel containing a flocculent able to agglomerate the suspended solidsto form agglomerations of the flocculent and the suspended solids uponexposure of the flocculent to a liquid input stream comprisingwhitewater or derived from whitewater, the flocculation vesselconfigured to produce a supernatant stream containing a lower quantityof suspended solids than the liquid input stream; a filter configured toreceive at least a portion of the supernatant stream, the filterconfigured to produce a retentate stream and a filtrate stream, thefiltrate stream containing a lower quantity of suspended solids than theretentate stream; and an ion exchange vessel configured to receive atleast a portion of the filtrate stream, the ion exchange vesselcontaining an ion exchange medium configured to remove at least aportion of the cations from the filtrate stream.
 2. The system of claim1, wherein the flocculation vessel comprises a magnetically responsivematerial configured to form agglomerations with the flocculent and thesuspended solids.
 3. The system of claim 2, wherein the magneticallyresponsive material comprises magnetite.
 4. The system of claim 1,wherein the flocculation vessel comprises a magnet configured to removeat least a portion of the magnetically responsive flocculentagglomerations from the liquid input stream.
 5. The system of claim 1,wherein the flocculation vessel comprises a gas input configured toinject gas into fluid contained within the flocculation vessel.
 6. Thesystem of claim 5, wherein the flocculation vessel comprises a dissolvedgas flotation separation apparatus.
 7. The method of claim 6, whereinthe dissolved gas flotation separation apparatus comprises a dissolvedair flotation separation apparatus.
 8. The system of claim 1, whereinthe flocculation vessel is configured to allow at least a portion of theagglomerations of flocculent and suspended solids to settle to thebottom of the vessel.
 9. The system of claim 8, wherein the flocculationvessel comprises a gravity settling clarifier.
 10. The system of claim1, wherein the filter comprises a disc filter.
 11. The system of claim1, wherein the filter comprises a screen filter.
 12. The system of claim1, wherein the filter comprises a strainer.
 13. The system of claim 1,wherein the filter comprises depth filtration medium.
 14. The system ofclaim 13, wherein the depth filtration medium comprises sand.
 15. Thesystem of claim 1, wherein the ion exchange medium comprises a weak acidcation resin.
 16. The system of claim 1, wherein the ion exchange mediumcomprises a strong acid cation resin.
 17. The system of claim 1, whereinthe filter is configured such that at least a portion of the retentatestream is recycled to the flocculation vessel.
 18. The system of claim1, comprising a total dissolved solids removal apparatus configured toreceive at least a portion of a liquid feed stream from the ion exchangevessel.
 19. The system of claim 18, wherein the total dissolved solidsremoval apparatus is configured to perform reverse osmosis. 20-70.(canceled)
 71. A method of treating whitewater, comprising: contacting aliquid stream comprising whitewater or derived from whitewater andcontaining calcium carbonate with an ion exchange medium; and adjustingor maintaining a pH of the liquid input stream at or below about 7.5such that at least a portion of the calcium carbonate is dissolvedwithin the liquid input stream prior to or while being contacted withthe ion exchange medium. 72-91. (canceled)